Snoring, upper airway resistance syndrome, and obstructive sleep apnea syndrome (“OSAS”) are all breathing disorders related to narrowing of the upper airway during sleep. Approximately 18 million Americans have sleep disordered breathing, but fewer than 50% are presently diagnosed. More than 50% of Americans over age 65 have sleep difficulties, and prevalence of sleep problems will therefore increase as the over-65 population increases. Each year, sleep disorders, sleep deprivation, and excessive daytime sleepiness add approximately $16 billion annually to the cost of health care in the U.S., and result in $50 billion annually in lost productivity.
Sleep disorders are largely caused by too much soft tissue in the throat. Humans are unique because their upper airway has a curved shape, an anatomical change that is related to the evolution of human speech. As a result, the upper airway on humans is more flexible than other species and is more prone to collapse under negative pressure. When awake, a certain amount of tone is present in upper airway muscles to prevent this collapse. However, during sleep muscle tone decreases in upper airway muscles and in certain susceptible individuals this relaxation allows the airway to collapse.
The upper airway refers to the air filled spaces between the nose and the larynx, and their surrounding soft tissue boundaries. For sleep disorders, the most relevant part of the upper airway is the air cavity called the pharynx.
The soft palate and the tongue are most susceptible to collapse because they are very flexible. The soft palate acts as a barrier between the mouth and the nose. The tongue is the largest muscular organ of the upper airway and is anatomically divided into a blade, body and base. Most of the tongue's curve is at the junction of the tongue body and base.
When the tone of the soft palate and tongue decreases during sleep, these structures become quite flexible and distensible. Without the normal muscle tone that keeps them in place, they tend to collapse at relatively low negative pressures. Although muscles relax throughout the body during sleep, many of the respiratory muscles remain active. Specifically, the major muscle that pulls the tongue forward, the genioglossus muscle, has been reported to show decreased activity during sleep, although it is active during obstructive apneas. Normally, the genioglossus is capable of moving the tongue forward and even projecting it out of the mouth. Why the genioglossus muscle fails to prevent obstructions has not been explained.
During inspiration, the chest wall expands and causes negative pressure to draw air into the nose and mouth and past the pharynx into the lungs. This negative pressure causes upper airway soft tissue to deform, further narrowing the airway. If the airway narrows enough, the air flow becomes turbulent causing the soft palate to vibrate. The vibration of the soft palate produces the sound known as snoring. Snoring is extremely common, effecting up to 50% of men and 25% of women. By itself, snoring is not a medical problem although it can be a tremendous problem for the snorer's bed partner and a major cause of marital strain.
A small amount of decreased airflow or brief obstructions occurs in all humans during sleep. These episodes are counted as medically significant if airflow is decreased more than 50% of normal (hypopnea) or if airflow is obstructed for more than 10 seconds (apnea). The number of apneas and hypopneas that occur during each hour of sleep is measured to diagnose the severity of the sleep disorder. These episodes of hypopnea or apnea often cause some degree of arousal during sleep. Although the patient does not awaken to full consciousness, the sleep pattern is disturbed causing the patient to feel sleepy during the day. If the frequency of hypopnea or apnea is more than 5 episodes per hour it is called upper airway resistance syndrome. These patients often show symptoms related to the sleep disruption. Specifically, these patients are excessively sleepy during the day. In addition, more subtle symptoms such as depression and difficulty concentrating are also common.
Technically, the diagnosis of OSAS is defined as an average of more than 10 episodes of hyponea or apnea during each hour of sleep. Although the airway is obstructed, the patient makes repeated and progressively more forceful attempts at inspiration. These episodes are largely silent and characterized by movements of the abdomen and chest wall as the patient strains to bring air into the lungs. Episodes of apnea can last a minute to more, and during this time the oxygen levels in the blood decrease. Finally, either the obstruction is overcome, usually producing a loud snore, or the patient awakes with the feeling of choking.
Very common symptoms in OSAS patients are morning headaches and acid reflux. During airway obstructions, the forceful attempts to inspire air can cause tremendous negative pressure in the chest. These high negative pressures can draw acid up the esophagus from the stomach. The acid can travel all the way into the mouth and cause inflammation of the vocal cords and nasal mucosa. The presence of the acid in the upper airway causes reflex bronchoconstriction in the lung that is similar to an asthma attack. If even a small amount of acid enters the lung it can cause the vocal folds to close tightly and itself cause a prolonged apnea called laryngospasm. In many patients the repeated stretching of the espophageal sphincter causes chronic changes and these patients can have acid reflux during the day.
Although OSAS occurs in both children and adults the cause and treatment are very different. OSAS in children almost always occurs when the child has large tonsils, and tonsillectomy cures the condition. Tonsils naturally decrease in size with age and are rarely a problem in adults. Instead, susceptible adults usually have enlargement of their tongues, soft palate, and/or pharyngeal walls. This enlargement is mostly due to fat deposits within these structures.
Adult sleep disorders are difficult to treat for a variety of reasons. The upper airway is a very mobile structure that performs the critical functions of swallowing and speech. These functions are easily compromised by surgical procedures or other interventions. In addition, the upper airway also has a large amount of sensory innervation that causes reflexes such as gagging and coughing. Theoretically, a physical stent that is placed in the oral cavity and pharynx would be completely effective in relieving sleep apnea. When a patient is totally unconscious, such as when they are anesthetized for surgery, the airway can be stented open by placing a curved oral tube into the mouth and pharynx. In addition, endotracheal tubes establish a secure airway for artificial ventilation. However, after anesthesia wears off, patients immediately sense and react to the foreign objects in their throats and expel them. Therefore, devices such as oral and endotrachael tubes, or anything similar, cannot be used for the treatment of OSAS.
Although physical stents cannot be used for OSAS, an indirect way of stenting the upper airway with positive air pressure is the most commonly prescribed treatment for OSAS. This method is called continuous positive airway pressure (“CPAP”). CPAP requires the use of a mask tightly attached around the nose and connected to a respirator. The exact amount of positive pressure is different for each patient and must be set by overnight testing using multiple pressures. The positive pressure acts like a stent to keep the airway open. CPAP is not a cure but a therapy that must be used every night. Although many OSAS patients are helped by CPAP it is not comfortable for the patient or their bed partner. Patients often cannot tolerate the claustrophobic feeling of a mask tightly attached to their face. In addition, there are often many technical problems with maintaining a proper seal of the mask to the face. For these reasons up to half of all patients who are prescribed CPAP stop using it within 6 months.
FIG. 1A is a schematic illustration of a prior art dental appliance 100. The dental appliance 100 is worn like a retainer and requires nightly compliance by the patient. The dental appliance 100 has an upper dental plate 102 and a lower dental plate 103. The dental appliance 100 also contains a fin-coupling component 105 that allows the mouth to open and close. The dental appliance 100 repositions the lower jaw slightly down and forward relative to the neutral position. This repositioning of the lower jaw forces the tongue to move further away from the back of the airway. Dental appliances generally have minimal efficacy.
FIG. 1B is a schematic illustration of a prior art Repose system 120. The Repose procedure is performed under general anesthesia and a screw (not shown) is inserted at the base of the mandible. The screw contains attachments for a permanent suture 125 that is tunneled under the mucosa of the floor of the mouth to the back of the tongue, then passed across the width of the tongue base, and brought back to attach to a metal hook (not shown) screwed into the bone of the mandible. The entire suture is located within the soft tissue of the tongue. The suture 125 is tightened to displace the tongue base forward, and caution must be observed to prevent excess tension leading to necrosis of tissue. A quantitative measurement of tension is not performed. Tension is estimated by a surgeon. Unfortunately, studies of the Repose procedure show that it is ineffective at eliminating OSAS. Only 1 of 15 patients was cured of OSAS while 2 patients had to have the suture removed due to pain and swelling.
FIG. 1C is a schematic illustration of a prior art Uvulopalatopharyngoplasty (“UPPP”) 130. UPPP is one type of surgical procedure that is available to shrink or stiffen the soft palate. UPPP excises excess soft tissue 135 of the pharyngeal walls and soft palate with a surgical scalpel. Because so much mucosa of the pharyngeal area is traumatized during a UPPP there is a large amount of post operative swelling and severe pain. In selected patients who snore but have no obstructions more limited versions of the UPPP can be done with lasers or electrical cautery.
One problem with some known devices and methods for the treatment of obstructive sleep apnea is that prior approaches have minimal or limited efficacy. Another problem is that prior approaches can be highly invasive, requiring significant, obtrusive, sometimes irreversible surgery, which can also lead to a high risk of infection. Another problem with some prior art solutions is that patients experience significant foreign body sensations when devices are placed in the patients' oral cavity as well as a negative social stigma when the foreign bodies are visible to the general population.
Accordingly, a need exists for improved methods and devices for the treatment of obstructive sleep apnea.